Alumina hydrate is a known adsorbent for several different halide ions and free radicals, including fluoride ions in aqueous solutions and fluoride, chloride, bromide, and iodide free radicals. When alumina hydrate is added to fluoride-containing dentifrices as a dental abrasive, untreated alumina hydrate particles will adsorb fluoride ions, thereby reducing fluoride concentration. It is thought that such reduction of fluoride concentration has a detrimental effect on caries prevention.
In Baines et al U.S. Pat. No. 4,098,878, there is disclosed a toothpaste containing alumina trihydrate abrasive particles which have been surface-treated with a long chain fatty acid or a mixture of such acids, or the corresponding alkali metal salt of such acids or mixtures. A preferred formulation relies upon surface treatment with stearic acid dissolved in acetone. Although this formulation successfully maintains an adequate fluoride ion concentration, the stearic acid is difficult to apply uniformly and may have an adverse taste if supplied in excessive amount.
In the prior art, sodium silicate has been added to dental cream compositions containing alumina abrasive material for the purpose of rendering the dental cream compatible with an unlined aluminum container. However, the pH conditions of sodium silicate addition were inadequate to prevent substantial reduction in luoride concentration by adsorption onto surface portions of the alumina. Dental cream compositions including both alumina and sodium silicate are disclosed in Mitchell et al U.S. Pat. Nos. 4,046,872; 4,075,317; and 4,152,417.
In another aspect of the present invention, alumina hydrate and halogenated hydrocarbon compounds are both known fire-retardant additives for flammable plastic resins. For example, Rodish U.S. Pat. No. 4,182,799 claims a flame-retarding additive for foamed polystyrene comprising 40-56 wt. % halogenated hydrocarbon, 16-23 wt. % alumina hydrate, 9-15 wt. % antimony oxide, and 14-22 wt. % zinc borate. The halogenated hydrocarbon inhibits flaming of the foamed polystyrene by generating halide-containing free radicals upon heating. However, alumina hydrate is a known adsorbent for such free radicals. Accordingly, there is a need to treat the alumina hydrate to reduce its adsorption of halide free radicals without affecting fire-retardancy of the hydrate.
It is a principal object of the present invention to provide a method for surface treating mineral particles that reduces adsorption of halide ions and halide free radicals onto surface portions of the particles. The mineral particles are preferably alumina particles.
A related object of the present invention is to provide alumina particles that are surface treated to reduce their adsorption of halide ions and halide free radicals.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following detailed description of our invention.